In general, internal combustion engines generate power by rotating the crankshaft while repeating four strokes composed of intake, compression, ignition or explosion due to fuel injection, and exhaust of a gas mixture or air. However, when the four strokes are continuously repeated, the fuel is continuously consumed for each four-stroke, such that fuel consumption increases, while the top of the cylinder block is exposed to significantly high temperature due to explosion repeated one time for each four-stroke. Accordingly, it is considerably difficult to cool the cylinder block and environmental pollutants are discharged with the exhaust gas.
A 6-stroke internal combustion engine has been proposed to overcome those problems, which uses power alternately generated by combustion of the fuel and by evaporation and expansion of injected water, by injecting water right into the cylinder block at relatively high temperature due to combustion of the fuel, right after the exhaust stroke.
According to the 6-stroke internal combustion engine in which intake, compression, explosion, exhaust, expansion, and re-exhaust strokes are sequentially repeated, since the fuel is consumed one time for not each four-stroke, but each six-stroke, fuel consumption can be considerably reduced in comparison to the 4-stroke internal combustion engine. Further, since water is injected into the cylinder block heated at high temperature by combustion of the fuel, the cylinder block is automatically cooled and the temperature of the exhaust gas is also decreased, such that it is possible to reduce to amount of environmental pollutants, such as NOx, which are produced in the exhaust gas.
However, the 6-stroke internal combustion engine having the configuration described above should generate power, using only expansion due to evaporation of the water, after generating by using combustion of the fuel. Therefore, the force produced by the expansion due to evaporation of the water is not enough to push the piston, such that sufficient power is not generated.
Further, in the 6-stroke internal combustion engine of the related art, thermal efficiency decreases, because the high-temperature exhaust gas produced by combustion of the fuel is discharged without being re-circulated.
In addition, the 6-stroke internal combustion engine of the related art usually injects water by using an electronic valve, and in this case reliability of water injection timing is deteriorated.